1. Field of the Invention
This invention relates to apparatus for tensioning a track chain of a tracklaying vehicle such as a bulldozer, crawler loader, or excavator, and more particularly to a hydraulic cylinder for biasing a reversing chain sprocket, which is rotatably mounted in a bearing that is displaceable in the vertical plane of the track chain.
2. Description of the Prior Art
In apparatus of the kind disclosed in U.S. Pat. No. 3,901,563, a hydraulic cylinder is supplied with fluid under the pressure that is required to tension to track chain. In order to avoid excessive tension in the chain, the hydraulic cylinder is connected by a relief valve and a check valve to a second cylinder chamber. The second cylinder chamber is filled with a fluid and contains a piston, which is biased by a prestressed spring, and which tends to urge the piston to a forward position defined by stop means. When the chain is under excessive tension, the pressure in the hydraulic cylinder rises above the normal pressure applied to tension the chain, and fluid will flow through the relief valve into the second cylinder chamber and will force the piston back so that the prestressed spring will be stressed further. When the tension in the chain decreases to below a normal value, the piston which is biased by the pressure of the prestressed spring forces fluid through the return valve back into the hydraulic cylinder until the spring has been moved into engagement with the stop means, which define the foremost position of the piston.
Published German Application 32 37 336 discloses track chain apparatus which includes control valve means for connecting a hydraulic cylinder to any of a plurality of relief valves so that the tension in the chain can be selected in dependence on different conditions of travel of the vehicle.
Although the known types of chain-tensioning apparatus can tension the chain in dependence on different operating conditions and can effect compensation for wear, a chain which is excessively tensioned during operation cannot be relaxed by the known apparatus to an optimum chain tension.
In apparatus of the kind described it is known that an optimum tension can be imparted to the chain if a chain-tensioning piston is associated with the hydraulic cylinder and is provided with a chamber that is filled with an elastomer and receives a plunger, which is connected to the piston rod that is used to bias the reversing chain sprocket so as to tension the chain. When it is desired to tension the chain, grease is manually pumped into the hydraulic cylinder until the movement of the piston rod of the plunger indicates that the chain tension has increased to a desired upper limit. To adjust the tension of the chain to an optimum value, the chain is subsequently relaxed in that grease is discharged through a manually operable valve. But that manual adjustment of the chain tension is complicated so that it is often omitted, and the grease or oil which has been discharged to relax the chain may fall on the soil, which is not desired.
For these reasons it is an object of the invention to provide track chain apparatus which is adapted to automatically adjust the claim to the optimum tension in dependence on the use and operating conditions of the vehicle.